Mirza and Zardari

Dr Zulfiqar Mirza is accusing his erstwhile leader Asif Zardari of all sorts of wrongdoing and corruption. It is not very clear why Dr Mirza has now become the worst enemy of Zardari after having been friends for 45 years.
Why has Asif Zardari, known for his policy of reconciliation and friendship, not able to maintain his friendship with Dr Mirza? Is this a kind of machination to weaken the PPP in rural Sindh? Why is Bilawal Bhutto quiet and not playing his role as PPP chairman to settle differences between two old friends? Whatever the result of animosity between Zardari and Dr Mirza, it is going to hurt the PPP in Sindh.
Engr S T Hussain
Lahore